How can you compare active and passive seismic control systems for structures?

1 Active systems

Active seismic control systems use sensors, actuators, and controllers to detect and counteract the seismic forces acting on a structure. They require external power sources and feedback mechanisms to adjust the stiffness, damping, or mass of the structure in real time. Some examples of active systems are active mass dampers, active base isolation, and active tendons. Active systems can provide high performance and adaptability, but they are also complex, expensive, and prone to failures or malfunctions.

2 Passive systems

Passive seismic control systems use inherent or added elements to dissipate or isolate the seismic energy without requiring external power or feedback. They rely on the properties of materials, geometry, or configuration to enhance the stability and resilience of the structure. Some examples of passive systems are base isolation, tuned mass dampers, friction dampers, and viscous dampers. Passive systems are simpler, cheaper, and more reliable than active systems, but they have limited effectiveness and flexibility.

3 Hybrid systems

Hybrid seismic control systems combine active and passive components to achieve a balance between performance and reliability. They use a passive system as the primary mode of control and an active system as a secondary or backup mode. They can also switch between modes depending on the intensity and frequency of the earthquake. Some examples of hybrid systems are semi-active dampers, semi-active base isolation, and semi-active mass dampers. Hybrid systems can offer the best of both worlds, but they also require more coordination and integration.

4 Selection criteria

The selection of a seismic control system for a structure depends on several factors, such as the seismic hazard, the structural characteristics, the design objectives, the budget, and the maintenance requirements. When making a decision, it's important to consider its effectiveness in reducing seismic response and damage, efficiency in terms of initial investment, operation, and maintenance, robustness under different scenarios and conditions, compatibility with the existing or planned structure and its functions, as well as sustainability in terms of environmental friendliness and social acceptability.

5 Comparison table

To help you compare active and passive seismic control systems, here is a summary table that shows some of their main features and trade-offs.

| Feature | Active | Passive | Hybrid |

|---------|--------|---------|--------|

| Power requirement | High | Low | Medium |

| Complexity | High | Low | Medium |

| Cost | High | Low | Medium |

| Reliability | Low | High | Medium |

| Performance | High | Low | Medium |

| Adaptability | High | Low | Medium |

6 Case studies

To illustrate how active and passive seismic control systems can be applied in practice, here are some examples. Taipei 101, a skyscraper in Taiwan, uses an active tuned mass damper to reduce the sway and vibration caused by wind and earthquakes. This damper is a 660-ton steel pendulum that moves in the opposite direction of the building motion, controlled by hydraulic actuators and sensors. San Francisco City Hall, a historic building in California, utilizes a passive base isolation system to reduce the seismic forces transmitted from the ground to the structure. This system consists of 530 rubber bearings and sliding plates that allow the building to move horizontally without affecting its stability. Billings Bridge in New Zealand uses a hybrid semi-active damping system to reduce the seismic response and damage of the bridge deck and piers. This system consists of magnetorheological fluid dampers that change their viscosity and damping force according to the applied magnetic field, controlled by a smart algorithm.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?